Method of making composite pistons



June, 2, 1931. H. E. DEPUTY fi fi METHOD OF MAKING COMPOSITE PISTONS Filed Aug. 20, 1928 florace Z Ie vu t Patented June 2, 1931.

PATENT OFFlCEz HORACE E. DEPUTY, OF DETROIT; MICHIGAN .EETHOD OF MAKING COMPOSITE PISTONS.

Application filed August 20, 1928., Serial No. 300,682.,

This invention relates to a process of making composite pistons, and has for its principal object the provision of a simple and effective method of making pistons of two or more metals. Preferably, I desire to combine a metal such as aluminum, or aluminum alloy, to secure the advantage of the relatively light weight, high heat conductivity, and adaptability for machining of such a metal, with a metal having a lower coefficient of expansion than the aluminum, or alloy thereof, such as cast iron, to overcome the usual disadvantage of aluminum pistons resulting from the relatively high e0 efiicient of expansion of aluminum and its rapid' wear when subjected to friction.-

Another object of the present invention is the secural of a substantially permanent bond between piston parts formed of different metals.

Other objects and advantages will be apparent from the following description of a preferred manner of embodying my method of making composite pistons, particular- 1y when taken in connection with the accompanying drawings, wherein: I

Figure 1 is a vertical sectional view through a piston constructed in accordance with my improved method.

Figure 2 is a cross section taken substantially on the line 2-2 of Figure 1, and Figure 3 is a detailed view of the sleeve before being bonded to the body portion of the piston.

In these views the reference character 1 designates the head of the piston, and 2 the relatively thick upper portion of the piston wall having the usual grooves 3 therein to .receivesealing rings (not shown). The numeral 4 designates an aluminum or aluminum alloy skirt portion of the piston formed integrally with the parts 1 and 2, while 5 designates a sleeve of cast iron, steel or other metal having a relatively low co-eflicient of expansion embracing the skirt portion 4. The sleeve or annulus 5 is rigidlyunited with the aluminum skirt portion of the piston throughout substantially its entire inner surface, and also the end faces of the sleeve abut and are preferably united with shoulders or flanges 7 and 8 integrally formed with the aluminum skirt portion of the piston.

I have found that by preparing a sleeve or annulus 5 of steel, cast iron or other metal having a relatively low co-eflicient of expansion and then placing such sleeve into the mold in which the aluminum portion of the piston is subsequently cast, that the aluminum body of the piston may be rigidly united with the sleeve. In the illustrated embodiment, the entire interior surface of the sleeve has been serrated by cutting a coarse screw-thread spirally along substantially the entire inner surface. The aluminum, when in its original molten state, enters fully between the serrations so asto firmly interlock the two metals. It is to be understood, however, that the sleeve 5 may be formed without any serrations, or that serrations or other forms than screw threads may be substituted for those shown.

To further insure a firm and substantialv ly permanent connection between the sleeve 5 and the aluminum skirt portion 4, it is preferred to subject the sleeve to'a preliminary acid bath so as to thoroughly cleanse the surface thereof, and then immerse the sleeve in molten zinc or tin so as to deposit on the sleeve in molecular union therewith a thin coating of zinc or tin. When subsequently the aluminum casting is hardening in contact with the sleeve, the coating also molecularly unites with the aluminum to fgm the bond between the sleeve and piston s 'rt.

A still further precaution may be exercised in the interest of an exceedingly rigid bonding between the two metal portions of the piston by highly heating the sleeve 5 preliminarily to pouring the molten aluminum into contact with the sleeve. This heatin may range from 400 to 1100 Fahrenheit, the temperature raise preferably being as great as may be employed without resulting distortion or burning of the bonding metals. As the two metals cool, the aluminum alloy will dissipate its heat more rapidly than the cast iron. and the contraction accompanying cooling of the sleeve 5 will increase the which consistsof providin a metallic sleeve, I and then provlding upon t e sleeve a deposit a of zinc alloy, then heating the sleeve to extons conslsting of first heatin tightness with which it embraces the aluminum. Such pre-heating of the sleeve 5 also avoids a too rapid chilling of the aluminum by the cast iron and such tendencies toward imperfections as might result.

In putting my inventionvinto practice, I first provide the desired serrations 6 upon the sleeve 5. I then treat the iron sleeve in an acid solution to cleanse same and remove all grease. The sleeve is then immersed in molten zinc or tin until a desired deposit has been secured thereon. The sleeve is then preheated to a desired relatively high temperature and properlyopositioned in the mold. The molten aluminum or aluminum alloy is then flowed into the mold in the manner well known to those skilled in this art. When the casting has set, the composite piston is preferably plunged into cold water to harden the aluminum or alloy. The mold and its core are, of course, shaped and designed so as to give the desired size and oontour'to the piston, it being understood that pistons of various sizes and shapes are intended to be lniade in accordance with my improved metho During the setting of the molten aluminum within the mold the zinc or tin deposit on the sleeve molecularly unites with the aluminum body portion of the piston adj acent the end faces of the sleeve as well as the entire inner peripheryiof the sleeve, thereby serving to effectively join the difi'ere'nt metallic portions of the pistons to eachother, and at the same time the shoulders or flanges 7 and 8 integrally formed with the body portion of the piston serve to definitely position the sleeve.

The piston may now be machined as desired. The piston illustrated herein is provided with the usual pair of diametrically opposed wrist pin bearings 9 which are shown as formed integrally with the aluminum body portion. It is to be understood, however, that other means of securing the wrist pin bearings in position may also be used.

What I claim is:

A 1. The process of makingcomposite pisa metallic sleeve to expand same, placin t e expanded sleeve in a heated mold, an then fiowin molten metalhaving a higher co-efiicient 0 expansion than the metal 'of'the' sleeve into the mold to engage the entire'inner periphery of the sleeve.

2. The process of making composite pistons pand same, then placing the expanded sleeve in a heated mold, and finally molding the remainder of the piston in engagement with the inner periphery of the sleeve.

In wltness whereof I hereunto set my hand.

HORACE E. DEPUTY. 

